Herbal (botanical) medicine involves the practice of prescribing plant products, or products derived directly from plants, for the treatment of disease. Herbal medicine has survived since prehistoric times, in part because, until recently, there were no effective alternatives. Some plants do contain biologically active ingredients, and some pharmaceuticals in widespread use today are identical to, or derivatives of, bioactive constituents of historic folk remedies. Indeed, herbal and botanical sources form the origin of as much as 30% of all modern pharmaceuticals.
Evidential support concerning use of plant products in veterinary patients is scarce and ranges from effective and safe to ineffective and risky. However, the methodologic quality of primary studies on herbal medicines for many species is generally poor. Trials usually lack firm endpoints, and periods of observation are usually short; the clinical relevance of the observed effects is not always clear. In addition, data that directly compare herbal remedies with well-established pharmaceutical products are often not available. However, as the database on herbs continues to grow, veterinarians seeking to prescribe natural, plant-based compounds should inspect the latest scientific literature for information on the compound or product of interest.
Making a rational decision about an herbal product requires knowledge of its active ingredients, its safety and adverse effects, and whether the herb has been shown to be as good as or better than pharmaceutical products available for the same purpose. This information is incomplete or unavailable for most herbal products. In addition, there are no standards or quality control testing of the products regularly recommended for animals. Risk versus benefit questions must be considered for products with unclear constituents and unknown active ingredients.
Botanical products come in a variety of preparations intended either for ingestion or external application. They may be fresh, dried, or freeze-dried; extracted and preserved in oil, alcohol, or water; and delivered as liquids, capsules, pills, poultices, or powders. Other forms of plant-derived substances include essential oils—volatile, rapidly evaporating oils obtained from the leaves, stems, flowers, seeds, or roots of a plant, commonly used in aromatherapy or massage.
The philosophical approach of the practitioner tends to dictate the type(s) of herbs prescribed. For example, North American botanical medicine evolved from European and Native American traditions relies more on pharmacologic actions than on folklore and metaphysics. In comparison, traditional Chinese veterinary medical (TCVM) herbology considers the supposed “energetic” nature of herbs. Western herbal prescribing practices incorporate physical examination findings akin to standard medical assessments, whereas TCVM recommendations depend heavily on the appearance of the tongue and the feel of the pulse. Instead of considering the pharmacologic effects of plants, TCVM practitioners rely on prescientific metaphors to describe the mechanisms of action of products prescribed. This, by definition, leaves them unaware of the actual biochemical processes occurring and is inconsistent with modern medical principles and ethics.
As aforementioned, herbs are plant-based drugs. However, they differ from pharmaceuticals by having a multiplicity of active, inactive, and unknown constituents with additive, synergistic, and/or balancing properties. The medicinal effects of herbs may vary from batch to batch as growing, harvesting, processing, and storage conditions change from year to year. These factors highlight the challenges of not only characterizing but also anticipating patient responses to plant-based prescriptions.
Herbalists recommend herbs for a wide range of disorders. For some conditions, the effects of plant-based drugs rival those of pharmaceuticals. There is evidence of effectiveness of botanical medicine for conditions ranging from digestive ailments to inflammatory conditions and immune support. Many herbs exhibit anticancer and antioxidant benefits. Veterinarians should consult the latest publications in medical literature to assess the strength of research for a condition in question, because the field and evidential support for a variety of conditions is growing rapidly.
Contraindications to the use of herbal products are mostly empirical and depend on the health status of the animal and the putative actions of the herb(s) under consideration. Situations warranting special caution include pregnancy, presurgical states in which the antiplatelet actions of plants interfere with coagulation, and cancer. That is, unforeseen herb-drug interactions could interfere with conventional care and cause unexpected results.
Rightly or wrongly, most herbal medicines are generally considered safe. However, because of the lack of manufacturing standards, quality control, and known effects in veterinary patients, herbal medicines probably present a greater risk of adverse effects and interactions than any other CAVM therapy. Harmful effects of herbs arise from intrinsic toxicity of the plant, herb-drug or herb-herb interactions, contaminants introduced during processing (eg, heavy metals, microbial contaminants, chemical toxins, or pesticides), intentionally added adulterants (eg, pharmaceuticals), or inappropriate prescribing. Examples of especially risky herbs with known toxicities include those containing pyrrolizidine alkaloids (eg, comfrey and chaparral); natural flea treatments made from pennyroyal, known to be lethal for small animals; and skin treatments containing tea tree (melaleuca) oil, which can cause severe neurologic manifestations and hepatotoxicity in cats if absorbed or consumed in sufficient concentrations. For many herbal poisonings, no antidote exists, making death from “natural” treatments such as herbs frustrating. Many Chinese mixtures have toxic components; their amount may be kept "secret" by the manufacturer as a proprietary ingredient. Substances such as strychnine (a neurotoxin) and aconite (a cardiotoxin) are not uncommon and pose particular risks to veterinary patients. The unwillingness of manufacturers to appropriately label bottles with the amounts of these toxic constituents raises the danger to patients and public health.
Before the development of modern pharmaceuticals, botanical-based treatments for veterinary patients were common, as evidenced by veterinary texts of the 19th and early 20th centuries. However, significant differences exist between historical and current use of these products. In the past, herbal products were used as treatment because underlying disease conditions had yet to be identified. Treatment “success” reflected elimination (or spontaneous resolution) of the problem. Because the underlying pathology was either vague or completely unknown, diseases with similar signs could not be differentiated. Veterinarians had few other approaches from which to choose. These factors make it exceedingly difficult to objectively evaluate the true utility of historically used herbal remedies; they also highlight the imprudence of placing undue faith in the prescribing practices of the past to determine treatments today.
Animal-based ingredients such as testes, penis, placenta, and horn found in Chinese “herbal” medicines harbor potential for zoonotic disease transmission. In addition to health concerns, animal-derived products in Chinese herbs contribute significantly to animal mistreatment and the endangerment of certain species. The unknown benefits of most mammal or insect ingredients currently do not appear to justify administering these agents to veterinary patients.